1. FIELD OF THE INVENTION
The invention relates to a portable platform trestle for assembly with similar platform trestles to form stages for public events, the platform trestle being manually adjustable as to height, adapted to be fold up into a flat package stackable with similar folded platform trestle to compact storage piles, and provided with a platform, a retangular upper frame, a lower frame and respectively two scissors on two opposite longitudinal sides, whereby the legs and the arms of the scissors are articulated with one end within the reach of corresponding corners of the upper and the lower frames and whereby the other end of said legs can be moved along lateral guideways of the trestle and arrested thereon for adjusting the height of the trestle.
2. DESCRIPTION OF THE PRIOR ART
Such platform trestles as are supported by way of scissors for the variable formation of stages, pedestals and platforms have been known in the prior art, for example, from the U.S. Pat. No. 4,047,594. Such known platform trestles are disposed directly side by side and are adjustable always to the desired level, whereby they are mutually interlocked. In practice, the known platform trestles proved very useful especially because of their high loading capacity and their little need of stowage capacity.
Nevertheless, the maximum height of the known platform trestles is limited to just under the half of their length so that for a usual length of eight feet the maximum height is of about three and a half feet. If the legs of the scissors were longer than the half of the length of the platform trestle, they would block each other and thus prevent the folding-up of the platform trestle. Moreover, with longer legs, the known platform trestle would not be rigid enough to support a charge of several tons, especially when affecting a corner of the trestle. After all, a stiffening of longer legs by enlarging their diameter would not be possible, because in that case the platform trestle would become too heavy so that it would not be carried and adjusted by two persons.
Furthermore, there have been known lifting stages from the U.S. Pat. No. 2,874,805 and the German Utility Model No. 18 39 223, the stages comprising respectively an upper platform and four scissor members, the legs of which are quite of the same length as the length of the platform. These known lifting stages are meant for lifting cars of similar, very heavy objects so that they have to be operated by motors or hydraulic means. The legs of their scissors are of quite a great diameter and thus very heavy so that they are completely stationary. A transport by two persons would be absolutely impossible.